You should be able to use BFGS to search for the optimal vector [r, g, b] [1]. BFGS estimates the hessian, and then takes a step in the right direction, so you

You should be able to use BFGS to search for the optimal vector [r, g, b] [1]. BFGS estimates the hessian, and then takes a step in the right direction, so you don’t need any derivatives (the score should be enough). [1] https://en.wikipedia.org/wiki/Broyden%E2%80%93Fletcher%E2%80%93Goldfarb%E2%80%93Shanno_algorithm?wprov=sfti1 https://en.wikipedia.org/wiki/Broyden%E2%80%93Fletcher%E2%80...